Converters for converting an analogue voltage signal to a corresponding digital value can be implemented using for example a sample and hold circuit. The sample and hold circuit samples and holds the analogue voltage signal at a predetermined sampling frequency. At a particular sampling period, an input charge is transferred from an input signal source, for example a source capacitor, to an input capacitor of the sample and hold circuit. Said input charge is proportional to the analogue voltage signal in said sampling period. In further digital processing of the converter a corresponding digital value can be assigned to each transferred input charge.
In some applications, for example in high accuracy converters for battery management systems monitoring a voltage output of a battery cell, the source capacitor can be part of a source low pass filter implemented at the input of the converter for attenuating spurious high frequency components which may be generating by neighbouring devices or by suddenly connecting or disconnecting several battery cells in parallel. The low pass filter has typically a cut-off frequency much lower than the predetermined sampling frequency of the sample and hold circuit. This causes the source capacitor of the low pass filter to discharge to the much smaller input capacitor of the sample and hold circuit. The discharge of the source capacitor causes a leakage of the input charge due to the transfer of the input charge to the sample and hold circuit, thereby degrading the accuracy of the converter.